As floor shape estimation prior art, there are known a technique described in Japanese Laid-Open Patent Application No. Hei 6 (1994)-31658 proposed by the applicant, and another technique mentioned on a paper entitled “Development of a Biped Walking Robot Adapting to an Unknown Uneven Surface” (Journal of the Robotics Society of Japan; Vol. 14, No. 4; May 1996).
The latter (i.e., that mentioned on the journal) will be summarized in the following and problems thereof will then be discussed.
In this prior art, the robot foot is configured to have three stories in height comprising an upper-foot plate, a cushioning section and a lower-foot plate (sole). The foot has potentiometers at four corners which detect the angle and the distance between the upper and lower-foot plates, and a clinometer (inclination sensor) which detects the absolute inclination of the upper-foot plate. The foot is also provided with spikes at the four corners.
In this prior art, when a free leg is landed, the foot is controlled to profile the floor surface based on the information obtained from the potentiometers and the clinometer. With this, the spikes (installed at the four corners) are in contact with the floor such that the lower-foot plate is in parallel with the floor surface. At that instant, the height and the angle of inclination of the floor are estimated through geometric calculation based on the detected absolute position and/or posture of the upper-foot plate obtained by the clinometer and the angle of the upper-foot plate relative to the lower-foot plate and the distance between the upper and lower-foot plates obtained based on the potentiometers.
However, this prior art technique has the following problems. Specifically, it can not conduct a posture stabilization control to manipulate the floor reaction force until the foot has landed on the floor to profile the floor surface. Further, if a member made of a soft material such as rubber is applied to the foot sole so as to enhance grip, the structure would disadvantageously increase estimation error.
Further, when the foot does not land on the floor completely, i.e., when the foot does not land with its sole surface-contact with the floor, it can not estimate a floor height correctly during the two-leg supporting period. Further, when the feet are in contact with the floor completely, for example, at the time of holding itself upright, it can not estimate, at the same time, the inclination of a surface with which each foot is in contact and a height difference between the surfaces with which the feet are in contact. Furthermore, since it can only estimate the floor shape at an instant of foot landing, if the floor deforms after landing, it can no longer estimate the deformed shape.
On the other hand, the former (i.e., that described in 6 (1994)-31658)) can estimate the inclination of floor, while conducting a posture stabilization control to manipulate the floor reaction force. However, during the two-leg supporting period it can only estimate the inclination of a surface that intersects or adjoins the surfaces with which the feet are in contact, whilst during one-leg supporting period it can only estimate the inclination of the surface with which the supporting leg foot is in contact. In other words, this prior art technique can not estimate the inclinations at the same time.